GOP Targets Minnesota Rep. Peterson, Whose District Voted for Romney in 2012; Democrats Do the Same to 14 Republicans

DETROIT LAKES, Minn.—Rep. Collin Peterson plays in a rock band named the Second Amendments. His staff includes a former GOP state legislator. He voted against the Affordable Care Act, and he worked with House Speaker John Boehner (R., Ohio) to hash out part of this year's farm bill.

For more than two decades, Mr. Peterson's conservative bent and focus on agricultural policy has helped him maintain his hold on the western Minnesota district he flies himself around in a Beechcraft Bonanza single-engine plane. But as one of just...